Effects of acute sublethal exposure to coumaphos or diazinon on acquisition and discrimination of odor stimuli in the honey bee (Hymenoptera: Apidae)

Two organophosphate compounds, coumaphos and diazinon, were examined for effects of sublethal exposure on odor learning and generalization in honey bees, Apis mellifera L. Using proboscis extension response training as a measure of odor learning and discrimination, a series of two experiments tested whether these compounds would inhibit bees from learning a new odor or discriminating between different odors. Bees were exposed to coumaphos or diazinon in acetone applied to the thorax, or to coumaphos or diazinon in hexane injected intracranially. At no dose tested or exposure method used was coumaphos shown to inhibit acquisition of a novel odor stimulus, although it was shown to slightly reduce discriminatory ability when given by intracranial injection. Diazinon had effects on odor learning at several small doses, and a small injected dose was shown to significantly inhibit learning of an odor stimulus paired with a sucrose reward. When bee head acetylcholineasterase activity was measured after dermal applications of both pesticides, only the higher doses of diazinon showed reduced activity, indicating that externally-applied coumaphos shows no significant effect on bee brain acetylcholinesterase activity. These data suggest that acute application of coumaphos has only slight nonlethal effects upon the behavior of honey bees and should have little effect upon bee tasks that involve odor learning.